/**
 * base64 编码
 * @param str
 * @return {string}
 */
function base64_encode (str) {
  let c1, c2, c3
  const base64EncodeChars = 'ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/='
  let i = 0
  const len = str.length
  let strin = ''
  while (i < len) {
    c1 = str.charCodeAt(i++) & 0xff
    if (i === len) {
      strin += base64EncodeChars.charAt(c1 >> 2)
      strin += base64EncodeChars.charAt((c1 & 0x3) << 4)
      strin += '=='
      break
    }
    c2 = str.charCodeAt(i++)
    if (i === len) {
      strin += base64EncodeChars.charAt(c1 >> 2)
      strin += base64EncodeChars.charAt(((c1 & 0x3) << 4) | ((c2 & 0xF0) >> 4))
      strin += base64EncodeChars.charAt((c2 & 0xF) << 2)
      strin += '='
      break
    }
    c3 = str.charCodeAt(i++)
    strin += base64EncodeChars.charAt(c1 >> 2)
    strin += base64EncodeChars.charAt(((c1 & 0x3) << 4) | ((c2 & 0xF0) >> 4))
    strin += base64EncodeChars.charAt(((c2 & 0xF) << 2) | ((c3 & 0xC0) >> 6))
    strin += base64EncodeChars.charAt(c3 & 0x3F)
  }
  return strin
}

/**
 * base64 解码
 * @param input
 * @return {string}
 */
function base64_decode (input) { // 解码，配合decodeURIComponent使用
  const base64EncodeChars = 'ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/='
  let output = ''
  let chr1, chr2, chr3
  let enc1, enc2, enc3, enc4
  let i = 0
  input = input.replace(/[^A-Za-z0-9\+\/\=]/g, '')
  while (i < input.length) {
    enc1 = base64EncodeChars.indexOf(input.charAt(i++))
    enc2 = base64EncodeChars.indexOf(input.charAt(i++))
    enc3 = base64EncodeChars.indexOf(input.charAt(i++))
    enc4 = base64EncodeChars.indexOf(input.charAt(i++))
    chr1 = (enc1 << 2) | (enc2 >> 4)
    chr2 = ((enc2 & 15) << 4) | (enc3 >> 2)
    chr3 = ((enc3 & 3) << 6) | enc4
    output = output + String.fromCharCode(chr1)
    if (enc3 !== 64) {
      output = output + String.fromCharCode(chr2)
    }
    if (enc4 !== 64) {
      output = output + String.fromCharCode(chr3)
    }
  }
  return utf8_decode(output)
}

/**
 * utf8 解码
 * @param utfText
 * @return {string}
 */
function utf8_decode (utfText) {
  let string = ''
  let i = 0
  let c = 0
  let c1 = 0
  let c2 = 0
  while (i < utfText.length) {
    c = utfText.charCodeAt(i)
    if (c < 128) {
      string += String.fromCharCode(c)
      i++
    } else if ((c > 191) && (c < 224)) {
      c1 = utfText.charCodeAt(i + 1)
      string += String.fromCharCode(((c & 31) << 6) | (c1 & 63))
      i += 2
    } else {
      c1 = utfText.charCodeAt(i + 1)
      c2 = utfText.charCodeAt(i + 2)
      string += String.fromCharCode(((c & 15) << 12) | ((c1 & 63) << 6) | (c2 & 63))
      i += 3
    }
  }
  return string
}

module.exports = {
  base64_encode,
  base64_decode,
}